1. Field of the Invention
This invention relates to a water-absorptive polyurethane fiber using a water-absorptive thermoplastic polyurethane resin material and to a method of producing the same. More particularly, this invention relates to an insoluble and nonionic water-absorptive polyurethane fiber with potential utility in environmental fields, including water treatment and deodorization, as well as in civil engineering, medicine and other fields, and to a method of producing the same.
2. Description of the Background Art
Known granular polymers exhibiting high water-absorptivity include resins obtained by subjecting a polyacrylic acid polymer, a polyvinylalcohol polymer or the like to a suitable degree of crosslinking, starch-graft resins, and the like. Among fibrous types are the so-called water-absorptive fibers, including acrylonitrile composite fibers having a carboxyl acid salt group introduced into a part of the surface layer, polyacrylic acid polymer fiber, anhydrous maleic acid fiber, polyvinylalcohol fiber, alginic acid fiber and the like (see Japanese Patent Public Disclosures No. 1-280069 and No. 3-279471).
The conventional water-absorptive fibers have the following drawbacks:
1) The water-absorptive fibers imparted with a carboxyl group or other ionic hydrophilic group become tacky upon water absorption and do not readily absorb ionic aqueous solutions and aqueous solutions containing an organic solvent. PA0 2) Most of the water-absorptive fibers have low physical strength upon water absorption and when imparted with a crosslinked structure to confer adequate physical fiber strength become fibers that are poor in water absorption and swelling. PA0 3) Most of the conventional water-absorptive fibers are short fibers that require a binder or the like when, for example, converted into the form of non-woven fabric, and, as such, are low in form impartibility. PA0 4) None offer a material having the excellent water retention, hydrophilicity, water absorptivity, biocompatibility and resistance to physical strength degradation upon water absorption that are needed for use in wide-ranging fields such as water treatment, deodorization, civil engineering and medicine.
Based on the results of a study directed to finding a solution to these problems, the inventors developed a method of producing a water-insoluble, nonionic water-absorptive polyurethane fiber of good processability that combines the properties of high water absorptivity, high biocompatibility and excellent physical strength.